Exercise bike



FIG. 1 is a perspective view of an exercise bike embodying the new design;

FIG. 2 is a front view thereof;

FIG. 3 is a back view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines in the figures illustrate the portions of the design that form no part of the claimed design. 

CLAIM The ornamental design for an exercise bike, as shown and described. 